It is known to use a flyback converter for operating an LED module. The flyback converter is part of an appropriate operating device and is operated, for example, in critical conduction mode, also called borderline mode. At the same time, the switch of the flyback converter is turned on on the primary side, so that in this activation phase the current on the primary side is constantly increasing. This results in a constant negative voltage on a detection coil at the flyback converter.
When the current has reached a predetermined peak value, the switch is turned off. After switch-off, the voltage on the detection coil jumps to a positive value, oscillates for a certain time period and then settles at a voltage corresponding to the output voltage Vout.
During this deactivation phase, the current on the secondary side decreases linearly. When the current on the secondary side reaches zero, the steady and preferably linear voltage on the detection coil drops. Thus, the voltage on the detection coil drops significantly when the current on the secondary side reaches zero. In the critical conduction mode, it is now necessary to be able to detect the zero point of the current on the secondary side to turn the switch of the flyback converter on again.
From prior art, it is known to monitor the voltage on the detection coil and compare it with a low predetermined restarting threshold. If the voltage on the detection coil falls below this threshold, it is detected that the current on the secondary side has dropped to zero and the switch on the primary side is turned on again.
In the technology according to prior art, the problem is that the actual time period until the zero crossing of the current on the secondary side cannot exactly be detected when such a fixed comparator threshold is selected.